Composition-dependent structural, microstructural and functional characteristics of fine-grained BaTi1-xHfxO3 ceramics consolidated by Spark Plasma Sintering

Abstract

The functional properties of BaTi1-xHfxO3 (0 ≤x ≤ 0.20) ceramics consolidated by spark plasma sintering from Pechini nanopowders are discussed in terms of the synergic effect of overlapping dissimilar structural modifications, nanoscale grain size reduction and ferroelectric-relaxor crossover. Structural and Raman investigations revealed the coexistence of various polymorph modifications. The main effects of Hf addition are: (i) a strong inhibiting of the grain growth process, (ii) the reduction of TC and increase of the orthorhombic-tetragonal and rhombohedral-orthorhombic transition temperatures until a single, "pinched" and diffuse ferroelectric-paraelectric phase transition occurs, (iii) a strong flattening of the permittivity maximum, (iv) a slight decrease of the grain boundary resistivity, but still allowing the application of high a.c. and d.c. fields and (v) a gradual reduction of polarization, hysteresis loops area, energy storage capability and tunability values. Based on the dielectric and thermo-Raman results, a new low-temperature phase diagram of the fine-grained BaTi1-xHfxO3 ceramics is proposed.